ABSENCE OF EARTHQUAKE CORRELATION WITH EARTH TIDES - AN INDICATION OFHIGH PRESEISMIC FAULT STRESS RATE

Because the rate of stress change from the Earth tides exceeds that fr om tectonic stress accumulation, tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the te ctonic rate and if rupture began soon after the achievement of a criti cal stress level. We analyze the tidal stresses and stress rates on th e fault planes and at the times of 13,042 earthquakes which are so clo se to the San Andreas and Calaveras faults in California that we may t ake the fault plane to be known. We find that the stresses and stress rates from Earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times. While the rate of earthquakes when the tidal stress promotes failure is 2% higher than when the stress does not, this difference in rate is not s tatistically significant. This lack of tidal triggering implies that p reseismic stress rates in the nucleation zones of earthquakes are at l east 0.15 bar/h just preceding seismic failure, much above the long-te rm tectonic stress rate of 10(-4) bar/h.